Revetment structure



March 5,1935. L R; MA ON 1,9 3,217

' REVETMENT STRT JCTURE.

Original Filed. Dec. 19, 1952 IINVENTOR. ndon Z? Mason the bankprotection of Portland cement concrete.

yatented Mar. 5, 1935 UNITED STATES- REVETMENT STRUCTURE Landon R.Mason, Los Angelcs, Calif., assignor to Union Oil Company of California,Los An: geles, Calif.-, a corporation of California Original applicationDecember 19, 1932, Serial No. 647,849. Divided and this application July1, 1933, Serial No. 678,663

5 Claims.

The present invention relates to revetments, earth dams, levees and liketypes of embankment protections and to methods for their construction.In particular, the invention relates to embankment protectionscontaining a bituminous mastic or concrete and .to pre-cast reinforcedslabs of asphaltic mastic or concrete for lining the surfaces of riverbanks, ditches and the like, and is a division of my co-pendingapplication Serial N 0. 647,849, filed Dec. 19, 1932. I

Among the types of embankment protections that have been developed foruse along the banks of rivers, ditches, levees, etc., is one using amattress composed of large pre-cast slabs of Portland cement concrete.These slabs are used for all of the sub-aqueous work and to some extentfor the work lying in the border zone just above the waters edge when itis at its lowest stage of flow. The upper bank protection is paved witha mat or sheet-oi Portland cement concrete. Aside from the fact thatthis type of bank protection is very expensive, it requires constantmaintenance due to the destructive action of water in flood times anddue to the impacts of floating logs, rolling stones and similar objectswhich are sufficient in some instances to completely destroy Moreover,the irregularities in the surface of the banks over which the Portlandcement concrete slabs are placed, caused either by poor grading or bythe washing away of the earth under the mattress of slabs or themonolithic mat, leaves the structure unsupported tosuch extent that aslight impact will effect cracking and destruction. Another cfsadvantageto the use of Portland cement concrete is the contracting efiect of theconcrete after expansion which results in cracking of the structure.Revetments constructed of Portland cement concrete thus require constantsupervision, repair and maintenance. In some places,

' such as along the'banks of the lower Mississippi River, large sums ofmoney are spent each year and after each flood to maintain the revetmentin repair from the damage caused by floods.

revetment which is self-healing when cracked and one which issufficiently flexible to follow the contours of the bank which itprotects.

Another object of this invention resides in'a revetment constructed of.an asphaltic mastic or concrete which is tough, dense, flexible andselfhealing. Another object resides in a method of constructingrevetments employing asphaltic mastic or concrete.

Another object is in a pre-cast revetment slab of great strength whichis lower in cost, more simple in construction and of greater durabilitythan any pre-cast revetment slab heretofore used.

It is another object of this invention to present a pre-cast slabadapted to use in revetment con struction made of asphaltic mastic orconcrete.

Other ancillary objects of my invention will be suggested in thefollowing description taken from the drawing and in the uses to which myinvention is put.

Referring to the drawing:

Fig; 1 is a perspective view of a pre-cast slab;

Fig. 2 is a section of the slab taken along line 22 of Fig. 1;

Fig. 3 is an end view of a revetment construction shown partiallyv insection;

Fig. 4 is an enlarged view of a portion of the mat on the slope shown inFig. 3; 4

Fig. 5 is a partial plan view of the mattress of slabs shown in Fig. 3;

Fig. 6 is an end view of a modified revetment construction.

In its broadest aspects, my invention comprises a revetment containingasphalt, and, in particular, filled asphalt. An'important feature of myinvention resides in a pre-cast slab containing filled asphalt which maybe employed in revetment construction, said filled asphalt being pref insuch proportions as to present a mastic of high tensile strength andresistance to impact and one which is self-healing when fractured.

More specifically, my invention comprises a revetment containing filledasphalt and comprising a mat or sheet containing asphaltic materialwhich is laid on the slope of an embankment to be protected againstwater action and comprising also a mattress of a plurality ofinter-locked precast slabs containing fllled asphalt ofhigh.tenerably'composed of-asphalt and a finely communi-l,

nuted filler such as diatomaceous earth combined 40 s.

sile strength and impact resistance atached to the em odiment in hingedrelation so as to follow the con ours of the surface over which it lays.

It is an important feature of my invention to present a revetmentcomprising filled asphalt and crushed stone or aggregate laid in theshape of a mat or sheet, said filled asphalt comprising a mixture ofbetween 5 and 30% of a filler such as diatomaceous earth and/or rockdust or other suitable filler and approximately 70 to 95% of a D gradesteam refined asphalt, said filled asphalt having a tensile strength ofapproximately 300 lbs. per square inch and an impact resistance ofupwards of approximately 2.5 ft. lbs. when mixed with Ottawa sand inamounts sufficiently to exactly fill the voids in the sand.

My invention also includes a method of constructing revetmentscomprising compacting a course of broken stone on an embankment to beprotected and filling the voids in the course of broken stone withfilled asphalt or asphaltic mas tic, then laying a second course ofbroken stone over the first course and filling the voids in the secondcourse with filled asphalt and preferably reinforcing the revetment withwire fencing or the like laid intermediate the first and second courses.

I have discovered that if banks to be protected are linedwith aspeciallydesigned bituminous mastic or concrete, the life of the revetment islengthened considerably due to the great tensile strength, resistance toimpact, permanent flexibility and self-healing properties of saidbituminous mastic or concrete. I have also discovered that if thepre-cast slabs of Portland cement concrete heretofore employed forrevetment con-- struction are replaced with pre-cast slabs ofasphalticconcrete or mastic, that a revetment is presented which is moreflexible than revetments constructed with the slabs of Portland cementconcrete.

The asphaltic concrete which I particularly desire to employ forpre-casting the slabs for use in revetments or for lining river banksand the like comprises a mixture of asphalt, a carefully selected andgraded finely comminuted filler or combination of such fillers, gradedsand and carefully graded, sharp, crushed stone. The combination ofasphalt and the filler shall herein be' referred to as filled asphalt orasphaltic mastic and the combination of the filled asphalt with sand thecementing agents for the crushed rock or aggregate are. described in myco-pending application, Serial No. 647,850, filed December 19, 1932.Briefly, these asphalts may be describedascomprising a mixture of Bgrade steam refined asphalt and a filler'such as diatomaceous earth orrock dust or a combination of such fillers. A "D grade asphalt is asteam refined asphalt havinga penetration of 40 to at 17 F.,-"a meltingor softening point of to 130 F. anda ductility be withinthespecifications but-the ductility is of greater than 100 at 77"; F.

The optimum concentrations and character ofv Softening point 175 F orover Penetration at 77 F 15 to 45 Penetration at F or less Ductility at77 F- 5 or over Tensile strength 300 lbs. per. sq. in. or over Impactresistance 2.5 ft. lbs. or over.

For determining the softening point, penetration and ductility of thefilled asphalt, the following methods outlined by the American Societyof Testing Materials shall be used:

Softening or melting point, ball and ring method D-36-26 PenetrationD525 Ductility D 11326T The tensile strength shall be determined bymaking one inch cubical briquets in molds commonly used for preparingtensile strength test briquets of Portland cement. The briquets shallbecomposed of standard 20 to 30 mesh Ottawa sand mixed with the properquantity of asphaltic mastic to exactly fill .the voids in the Ottawasand which comprises 32 by volume. After the briquets have cooled theyshall be placed for one hour or more in a water bathat 77 F. and shallthen be pulled apart in a suitable testing machine for determiningtensile strengths.

The impact resistance shall be determined by making two inch cubicalbriquets in molds and the briquets shall be composed of standard 20 to30 mesh Ottawa sand mixed with the proper quantity of asphaltic masticto exactly fill the voids in the Ottawasand which comprise 32 /2% byvolume. After the briquets have cooled, they shall be placed for onehour or more in a water bath at 77 F. and shall be tested by dropping atwo inch steel ball weighing 1.175 lbs. upon the cube, allowing the ballfirst to drop six inches and then progressively increasing the height of'fall one inch per blow until destruction of the cubefined asphalt and28 to 70% by weight of filler or combination of fillers, such asdiatomaceous earth and rock dust, as determined in my above mentionedco-pending application. For example, a

filled'asphalt composed of 72% by weight of asphalt and 28% by weight ofdiatomaceous earth will conform with the-above specifications as tosoftening point, penetration, ductility, tensile strength and impactresistance. Likewise, a mixture 'of 57% asphalt, 21 /2'% diatomaceousearth and 21 rock dust and also a mixture of equal parts of asphalt andfiller where thefiller comprises equal parts of diatomaceous earth androck dust will have such specifications as indicated above but it willbe observed that the ductilities of mixtur containing rock dust are lessthan when using straight diatomaceous earth. A mix-- ture of 30% asphaltand 70% rock dust will also Passing a 200 mesh sieve 6-8 Passing an 80mesh sieve 14-20 Passing a 40 mesh sieve 26-34 Passing a 10 mesh sieve36-44 Passing a 3 mesh sieve.. 54-64 Passing a screen with V in.circular openings 78-88 Passing a screen with A in. circular openings95-100 In admixing filled asphalts with commercial aggregates, careshould be taken to adjust the percentage of filled asphalt to exactlyfill the voids in the aggregate since the maximum tensile strength andresistance to impact is obtained ume of the aggregate.

It is preferable to choose an aggregate having I a maximum density, thatis, having a minimum of voids. By carefully proportioning the amount ofsand to crushed rock, it is possible to obtain an aggregate having aminimum of voids. I have found that an aggregate composed of crushedrock capable of passing a screen having inch circular openings andgraded sand in the proportion 50.5% to 49.5% by volume, respectively,has a smaller percentage of voids, i. e., approximately 20.5% by volumethan any other combination of these materials. Consequently,approximately 20.5% by volume of asphalt will exactly fill the voids ofthis aggregate to produce an asphaltic concrete of maximum density.

Thepre-cast slab 10 of asphaltic concrete 01' mastic shown in Figs. 1and 2 are approximately ten feet long, six feet wide and from two tofour inches thick. The slab is preferably built in several coursesll and12 of asphaltic concrete or mastic and is provided with several rods 14of steel, iron or other suitable metal which are placed diagonally inthe center of the slab as shown. Each rodis preferably provided withrings 15 on each end protruding from the corners of the slab to permitinterlocking at the four corners with adjacent similar slabs by means'ofcables, rings, clips and like fastening devices.-

The slab is provided with suitable reinforcing 16 extending centrallythrough the slab. I

Pre-cast asphaltic concrete slabs 10 may be constructed according to thefollowing method:

A rectangular steel form of the required dimensions for the slabs, suchas to length, vwidth and thickness and similar to the forms used inconstructing slabs of Portland cement concrete is placed on a levelsurface of such material as will prevent sticking of the slab to beconstructed to the surface. If desired, the surface may be covered withmanila paper in order to prevent bonding of the slab to the sugface.Steel or iron rods 14 of about inch in diameter provided at each endwith rings 15 and somewhat longer than the diagonal length of the formare placed diagonally across the form in such manner as to permit theends to protrude out of the corners of the form. The rods are placedabout half way into the thickness of the form. One way of permitting therods to be placed half way into the form is to slit the corners of theform to the required depth so as to permit the rods to rest at thecorners of the form. If desired, the intersection 17 of the diagonallyplaced rods may be tied with wire. Asphaltic concrete composed of filledasphalt, graded sand and crushed rock at a temperature of 250 to 450 F.is then poured into the mold and is tamped-to exactly fill the mold.After the asphaltic concrete has cooled and hardened sufficiently topermit its removal, the slab is removed from the mold. The asphalticconcrete is preferably prepared by first forming the filled asphalt bymixing asphalt and filler at a temperature of 350 to 500 F. and thenmixing the filled asphalt while hot with the aggregate which has alsobeen heated to temperatures approximating that of the asphalt. Ifdesired, approximately 20% by volume of the filled asphalt composedofequal parts by weight of asphalt and filler where the filler comprisesequal parts by weight of diatomaceous earth and rock dust may be mixedwith approximately by volume of aggregate composed of crushed rock andsand. Preferably, I desire to employ a filled asphalt composed of 28%by'weight of diatomaceous earth and 72% asphalt because it is possibleto use more asphalt when'using diatomaceous earth to produce a filledasphalt of a given high tensile strength and ductility than when usingrock dust either alone or in admixture with diatomaceous earth.Moreover, diatomaceous earth absorbs the oils in the asphalt andprevents evaporation of the oils by the sun or atmosphere, thus givingthe revetment a longer lifethan when using coarser fillers alone whichdo not possess this phenomenon except to a minor degree.

A preferred method for constructing pro-cast asphaltic concrete slabs isas follows:

After placing the form on a suitable surface, as stated previously, acourse 11 of one to two inches of crushed stone of such size as to passa screen of inch circular openings is placed in the form. The rods 14are then placed in the form and filled asphalt of the above statedcomposition, i. e. 50% asphalt, 25% diatomaceous earth when the slab hascooled and hardened sufficiently to permit removal, it is removed fromthe form and is ready for use. If desired, screen- 'ings 18 may'also beprovided for the lower face of the slab by placing them in the moldprior to the building up of the slab.

If desired, and the same is quite preferable, re-

inforcing 16 is placed between the first and second courses 11 and 12ofcrushed rock and filled asphalt is preferably placed on the first courseof crushed stone prior to filling the voids with filled asphalt. Thereinforcing may consist,

of any acceptable wire-fencing or any other type of inter-woven orfabricated'wire orcotton or jute mesh. This is to be placed between thecourses of the crushed rock and filled asphalt and should be thoroughlycovered with filled asphalt so that it will be bonded'to the coursesbetween which it lays. The mesh of the fabric used should large enoughto permit the interlocking of the courses between the mesh. If anon-metallic mesh is used, the material should be saturated with asphaltor asphalt containing finely divided mineral filler.

The above described pre-cast slabs are employedin revetment constructionknownas'buttslab revetments, that is, where the ends of each slab areabutted against adjacent slabs and are held together by means of cables,rings or clips passed through the rings protruding from the corners ofthe slab. In such cases, the metal rods carrying the loops to permitjoinder of adjacent butt-slab revetments are necessary. However, I donot wish to be limited to the exact mode of placing the rods in the slabsince the rods may be placed in other directions in the slab than byplacing them diagonally across the slab. It is entirely possible toconstruct revetments of the lap-slab type, that is, where the slabs arelaid like shingles on a roof, the lower end of the upper slaboverlapping the upper end of the lower slab by approximately one foot.In such cases, the slabs are constructed without the metal rods sincethe slabs are retained in position by the weight of the over-lappingslabs.

In order to determine some of the characteristics of slabs constructedof my asphaltic concrete, I have made certain tests which show thedesirability of using pre-cast slabs of asphaltic concrete forrevetments rather than slabs of Portland cement concrete. I have madeslabs of asphaltic concrete 2'? inches wide, 36 inches long and 2 inchesthick in a manner similar to that disclosed above for making slabs foruse in revetments. However, the steel rods were omitted but thereinforcing was-used. For example, a one inch course of small crushedstone was placed in the form and filled asphalt composed of 12% byweight of D grade asphalt and 28 by weight of diatomaceous earth at450,F. was poured by means of a pouring pot over this course in amountssufficient to fill the voids inthe crushed pared. The concrete had acomposition by weight of one part Portland cement to four parts ofclean, sharp, graded sand which is used by the U. 8. Government to linethe banks of certain rivers. A concrete of this composition is strongerthan concrete containing one part Portland cement,

two parts sand and four parts crushed stone. These slabs were cured forseven days 'under water prior to testing. j v

After seven days of aging, a slab of Portland cement concrete and a slabof asphaltic concrete were 'subjectedto impacts of a falling hammerweighing ten pounds dropped from a height of three feet. Each of theslabs to be tested .were

removed from its-form and. placed on a dry sand bearing three to fourinches thick and in such position that when the hammer was allowed tofall, it struck exactly in the center of the slab. The hammer was thenstruck upon the slab from a height of three feet. 'On the second blowfrom three feet, the Portland cement concrete slab cracked through itsentire length and was held together merely by the reinforcing. It wascompletely destroyed afew blows thereafter. The reinforced asphalticconcrete slab was then tested in exactly the same manner after firstthoroughly chilling it by cooling it with cold water in order to makethe test as drastic as possible and to imitate practical conditions. Onehundred brows from a height of three feet produced no fracture whateverand merely beat down a slight deression under the hammer due chiefly tothe smashing of the screenings which formed the upper course of theslab.

To illustrate the flexibility of the asphaltic concrete slab, it wasplaced acrossa pileof sand so that the slab was supported only at itscenter. The results of this test showed that although the slab bent tofollow the contour of the sand pile, it did not crack. To illustrate theself-healing characteristics, the slab was purposely cracked by a sharpblow and was then placed on a flat surface and in a short course oftime, the crack disappeared.

Tensile strength tests performed by pulling apart one inch cubicalbriquets 'in the manner stated above and composed 0f 32 /z% by volume offilled asphalt comprising 28% by weight diatomaceous earth and 72% byweight asphalt and 67 by volume Ottawa sand showed tensile strengths ofapproximately 400 lbs. per square inch, whereas similar tests on' oneinch cubical briquets of one part Portland cement and three parts Ottawasand revealed tensile strengths of merely 210 lbs. per square inch.

It is thus apparent that pre-cast revetment slabs of filled asphalticconcrete are superior to those made of Portland cement concrete withregard to tensile strength, resistance to impact and flexibility.Furthermore, asphaltic concrete slabs are superior with respect to theself-healing property after fracture which, of course, is not apparentin the Portland cement concrete slabs.

An example of the method for constructing a reinforced asphalticconcrete revetment is as follows:-

After the slope of the bank 19 (Figl 3) is carefully graded to a 1 on 2to 3 slope, a mat 20 of asphaltic'material is placed on the bank. Thismat is constructed by spreading a course 21 of broken stone 22 of 1 to 3inches in thickness over the embankment or slope to the toe of the bank.The stone is then compacted and brought to a proper cross-section. Inthis construction, the sand forming the smaller aggregate may beomitted, if desired. Reinforcing 23, such as any acceptable type ofmalleable wire fencing or any fabric such as that used for reinforcingthe above described pre-cast slabs, is then tightly and evenly stretchedover this course of broken stones.

I prefer to employ a mesh of No. 9 gauge wire having the mesh spaced 6to 12 inches apart. The mesh may be either tied with wire at its jointsor it may be spot welded. The wire netting may earth and/or othersuitable fillers, such as rock dust, is then applied over the brokenstone and reinforcing until all of the voids are filled and the surfaceis completely coated. Any suitable means, such as pumping, spraying orpouring, may be used for. applying the filled asphalt to the course ofbroken stone and reinforcing wire. The amount of filled asphalt requiredwill vary from one-half to three gallons per square yard depending uponthe percentage of voids in the course. The percentage of. voids isdependent upon the thickness of the course, size of stone used and otherfactors. In every case as much asphalt should be used as can be held bythe first course and reinforcing without runningdown the slope.

A second course 25 of broken stone 26 is then spread evenly over theprepared base course and is compacted by tamping or rolling until thebottom of the top course adheres to and is interlocked with the basecourse and reinforcing. This i one inch in diameter.

top course may be from 1 to 2 inches in thickness.

. A second application of the filled asphalt is then over the entiresurface and the entire surface is compacted by tamping or rolling.

It will be observed by reference to Fig. 4 that the broken stone 22employed for the base course may be larger than the broken stone 26 ofthe top course. For example, the base course may be prepared with brokenstone capable of passing circular openings in diameter equal to thethickness of the base course, whereas the crushed stone used for the topcourse may be of such size as topass a screen having circular openingsof If desired, smaller size crushed stone, such as will pass a screenhaving circular openings of one-half inch diameter may be mixed with thebase course of broken stone to fill the voids in the broken stone priorto the application of the filled asphalt. Likewise, sand and/or gravelmay be worked into the base course. Gravel and/or sand may also be mixedwith the crushed stone of the top course prior to the spraying of thecourse with filled asphalt.

It is preferable to provide the toe'of the slope with a thick wall 30 ofabout one foot thick of asphaltic concrete extending several feet intothe ground. The purpose of this is to prevent water from washing theearth under the asphaltic mat particularly at the toe of the slope.

If desired, and where the slope of the bank to be protected permits, thebank may be lined with .a prepared mixture of hot asphaltic concrete ina manner similar to the pavement 9f roads with asphaltic concrete. Inthis case, a layer of asphaltic concrete is first applied and tamped andthe reinforcing mesh is then stretched over this course. Then a secondcourseof hot. asphaltic concrete is applied over the reinforcing meshand the whole structure is tamped and rolled. The asphaltic concreteemployed may comprise a mix- .ture of filled asphalt and aggregateprepared by hot mixing as stated above. The aggregate employed'i'orthelower coursemay be considerably larger than that used in the asphalticconcrete of the top course but in all cases the amount 7 actly fill thevoids in the aggregate.

erably lined with a mattress of pre-cast slabs of asphaltic concretemade in the manner described above. Each slab is interlocked or fastenedto adjacent slabs by means of cables, rings or clips 31 passed throughthe rings provided on the slabs as shown in plan in Fig. 5. The slabsare preferably laid with their lengths parallel to the bank. Themattress composed of a plurality of slabs interlocked, as stated, istied to the 'embankment in hinged relationship by means of cables orwire 32 passed through the rings l5 of the slabs adjacent the toe of theslope and the ring of anchors 33 which are embedded in the asphalticconcrete at the toe of the slope. A mattress of this character is quitefiexible and will follow the contour. of the surface over which it islaid should the earth. under the slab structure be washed away.

If desired, instead of a butt-slab mattress as described above, alap-slab mattress may be employed for lining the river bed below the toeof the slope. .In such cases, the pre-cast slabs 10 are laid in much thesame manner as the laying of shingles on a roof and as shown in Fig. 6.

' An over-lap 40 of approximately one foot is sufiicient to retain theslabs in place. When' the river bed is dry, it is desirable to cementthe over lapping section 40 to the lower slab by means of an asphalticcement. This type of structure is also quite. flexible and should earththereunder be washed away, it also will follow the contour of thesurface.

While the above invention has been described using D grade asphalt asthe preferred grade of asphalt, it is evident that other grades ofasphalt may be employed to produce the filled asphalt for the abovementioned uses. Nor is the invention limited to a filled asphalt as theplastic ingredient or cementing agent since unfilled asphalt, air blownor emulsified asphalt may be used. Furthermore, other bituminousproducts having more or less cementing characteristics may be employedsuch as cracked and uncracked petroleum residues, cracked and uncrackedcoal tar residues, pitch, tar and the like.

The above disclosure is to be taken as merely illustrative of apreferred embodiment of my invention and is not to be consideredlimiting, since many variations thereof may be made within the Scope ofthe following claims.

1. A revetment structure for protecting the slope of anembankmentcomprising a course'of stones laid on the embankment andfilled asphalt filling the voids in said course, said filled asphaltcomprising 15 to 25 percent by volume of the mixture of filled asphaltand stonesin said course.

2. A revetment structure for protecting the slope of an embankmentcomprising a course of stones laid on the embankment, asphalt fillingthe voids in said course and a second course of smaller stones laid onsaid first-mentioned course with filled asphalt filling the voids insaid second course, said filled asphalt comprising 15 to 25 percent byvolume of the mixture of filled asphalt and stones in said secondcourse.

3. A revetment structure for protecting the slope of an embankmentcomprising a course of stones laid on the embankment, filled asphaltfilling the voids in said course and a second course of filled. asphaltused should be sufiicient to ex-'T-'0 small r st nes laid .on' said fi s-mention d course with-filled asphalt filling the voids in said secondcourse, said filled asphalt comprising 1,5 to 25 percent by volume orthe mixture or filled asphalt and stones in the courses.

4. A revetment structure for protecting the slope of an embankmentcomprising a course of stones laid on the embankment, asphalt fillingthe voids in said course, reinforcing wire laid on said course and asecond course of smaller stones laid on said first-mentioned course withfilled asphalt filling the voids in said second course, said filledasphalt-comprising 15 to.25 percent by volume of the mixture of filledasphal and stones in said second course. L

laid on said course and a second course of smaller stones laid on saidfirst-mentioned course with filled asphalt filling the voids in said.second course, said filled asphalt comprising 15 to 25 percent byvolume or the mixture of filled asphalt and stones in said courses.

LANDON R. MASON.

